1. Field of the Invention
The invention relates to an arrangement for coding color television signals comprising:
means for providing a luminance signal and first and second color difference signals; PA1 a three-dimensional filter circuit coupled to receive said luminance signal, for providing a filtered luminance signal; PA1 first and second three-dimensional sub-filters, coupled to receive said first and second color difference signals, respectively, for providing filtered color difference signals, said first and second sub-filters each being constituted by a series arrangement of a low-pass filter and a combined vertical-temporal filter; PA1 a quadrature modulator for converting said filtered color difference signals into a modulated chrominance signal; and PA1 an adder circuit for adding together said filtered luminance signal and the modulated chrominance signal. PA1 a quadrature demodulator for converting said modulated chrominance signal into first and second color difference signals, PA1 a three-dimensional filter circuit coupled to receive said luminance signal, and PA1 a three-dimensional filter circuit coupled to receive said first and second color difference signals.
In addition, the invention relates to an arrangement for decoding color television signals including a luminance signal and a modulated chrominance signal, comprising:
The invention also relates to methods of transmitting color television signals using an arrangement for coding color television signals and an arrangement for decoding color television signals.
2. Description of Related Art
The periodical "Radio mentor", Vol. 12, 1969, pp. 847-851 discloses an arrangement for encoding color television signals in accordance with the
standard. In this prior art arrangement a notch filter is arranged in the path of the luminance signal. This notch filter has for its object to provide that at the receiver side on demodulation of the chrominance subcarrier luminance portions are not erroneously evaluated as chrominance signals, that is to say converted to a lower frequency and consequently produce low-frequency chrominance noise.
The periodical "Fernseh und Kinotechnik", 39.sup.th edition, Vol. 3, 1985, pp. 123-135 describes a digital PAL-Codec (PAL-coder and PAL-decoder) with improved luminance-chrominance separation. Using this digital PAL-codec disturbing cross-color and cross-luminance effects such as they occur in the PAL-codecs disclosed as prior art in said periodical, can be reduced or prevented. To achieve this, the article basically proposes to provide, in addition to the band limitation to approximately 5.5 MHz in the f.sub.x direction which is provided anyway, a combined vertical-temporal prefiltering and post-filtering operation. Together these measures result in a three-dimensional implementation of the luminance and chrominance signals such that both the luminance and also the chrominance components are allocated unambiguous positions in the three-dimensional frequency space, so that at the receiver side a highest possible error-free separation of the luminance and chrominance components is enabled.
In addition, the U.S.-4,683,490 discloses an arrangement for coding color television signals in a NTSC color television transmission system, in which inter alia a three-dimensional filter circuit is always arranged in the luminance channel and in the chrominance channels. The three-dimensional filter circuit in the chrominance channels comprises three-dimensional sub-filters, which are constituted by a series arrangement of a low-pass filter and a combined vertical-temporal filter.